Soil erosion is a phenomenon occurring in a wide variety of situations. It is accelerated by the action of wind and of rain and is especially bad in conditions of poor soil coherence. The loose surface is scuffed by the wind and seeds of plants that might otherwise germinate to provide a root system to hold the soil in place are disturbed. In like fashion streams of water formed in rain storms on less pervious soils carry away the surface.
In the making of cuttings, embankments, or culverts during highway construction, large areas of steeply sloping bare soil are exposed to the weather. The construction engineer has commonly distributed a layer of straw over the surface. However, that is susceptible to loss by wind. More recently asphalt emulsions have been applied to the straw layer to hold the stalks in place. Those emulsions are undesirable because of application difficulties such as a need for heat source, plugging of the application equipment and creating a major clean-up problem.
The straw serves another function as an insulator to protect newly emerging grasses from frost when the seeding is done in the spring or late fall. Also, straw is available in the near vicinity of where needed.